Modern electronic devices such as a notebook computer comprise a variety of memories to store information. Each memory cell may require at least a capacitor to retain information. According to common practice, metal-oxide-metal (MOM) capacitors can provide adequate capacitance for integrated circuits such as memory circuits. A single layer MOM capacitor may comprise a first metal plate, a second metal plate and an insulation layer deposited between the first metal plate and the second metal plate. The capacitance of the single layer MOM capacitor is proportional to the area of the metal plates and the dielectric constant of the insulation layer.
In order to provide a larger capacitance while keeping a smaller die area of a MOM capacitor, the MOM capacitor may include a plurality of layers stacked together. A multilayer MOM capacitor may comprise two electrodes. Each electrode is coupled to a plurality of fingers, each of which and its corresponding finger coupled to the other electrode form a sub-capacitor. On one layer of the MOM capacitor, various sub-capacitors are formed by a variety of neighboring fingers. The total capacitance of each layer is equal to the sum of the sub-capacitors on this layer. Furthermore, the electrodes of the multilayer MOM capacitor connect all layers together through a plurality of via plugs. As a result, the total capacitance of the multilayer MOM capacitor is equal to the sum of the capacitances of all layers of the multiplayer MOM capacitor.
The semiconductor industry has experienced rapid growth due to improvements in the integration density of a variety of electronic components (e.g., transistors, diodes, resistors, capacitors, etc.). This improvement in integration density has come from shrinking the semiconductor process node (e.g., shrink the process node towards small feature sizes, such as 65 nanometers, 45 nanometers, 32 nanometers and below). Semiconductor technologies with small feature sizes lead to more interactions between semiconductor fabrication and design. For example, the impact of moisture stored in a MOM capacitor will become more important for devices with small feature sizes. The moisture stored in a MOM capacitor must be lowered down to a minimum level so as to ensure the devices with small feature sizes meet the performance index to which they are specified.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.